Video compression system

ABSTRACT

A video compression system is disclosed that is optimized to take advantage of the types of redundancies typically occurring on computer screens and the types of video loss acceptable to real time interactive computer users. It automatically adapts to a wide variety of changing network bandwidth conditions and can accommodate any video resolution and an unlimited number of colors. The disclosed video compression encoder can be implemented with either hardware or software and it compresses the source video into a series of data packets that are a fixed length of 8 bits or more. Sequences of one or more of these packets create unique encoding “commands” that can be sent over any network and easily decoded (decompressed) with either software or hardware. The commands include 3 dimensional copying (horizontal, vertical and time) and unique efficiencies for screen segments that are comprised of only two colors (such as text). Embodiments are also disclosed that improve the video compression depending on the popularity of pixel colors.

FIELD OF THE INVENTION

This invention relates to computer data processing, and moreparticularly to computer video compression.

BACKGROUND OF THE INVENTION

Existing video compression systems can compress a stream of video dataso it takes less bandwidth to send over a communication channel. Suchsystems take advantage of redundancies expected to occur in the videothey are aiming to compress. For example, JPEG and MPEG take advantageof frequent similarities in the colors of adjacent pixels inphotographic images. In addition, MPEG takes advantage of the fact thatmotion pictures often have many pixels that stay the same color duringmany frames of video or only shift their positions on the screen as thecamera moves.

Video can be further compressed depending on how much degradation invideo quality (or “video loss”) is acceptable to the person (or “user”)viewing the video, but the acceptability of different types of videoloss is highly dependent on the user's activity (or “application”). Thefour types of video loss are; (1) resolution loss (appears blurred), (2)color depth loss (has fewer shades of colors), (3) frame rate loss(stalling or jerkiness of a motion picture) and (4) time loss or“video-delay” (time delay from video capture to its availability forviewing).

To achieve higher compression ratios, different compression systems takeadvantage of the types of video loss that are the most acceptable to theusers they aim to satisfy. For example, with MPEG, fast action scenesthat would generate too much data for the communication channel are sentwith resolution loss because movie viewers accept resolution loss betterthan they accept frame rate loss or color depth loss.

Video delay is not a problem in some applications but it is a seriousproblem in other applications. Different compression systems imposedifferent amounts of delay as they compress the video. Systems thatimpose more delay achieve higher compression ratios because all thevideo frames captured, held and examined during the delay provide abetter opportunity to decide how to compress them. One example might be:“is the camera moving or is just one object in the scene moving”.

Video delay is not a problem with “one-way” user activities, such aswatching movies; therefore, the compression systems used for theseapplications (such as MPEG) impose a long delay (many seconds or more)before compressing the video and beginning to send it over thecommunication channel. In fact, when the communication channel is anetwork with indeterminate bandwidth availability (such as theInternet), the video received from the network is often buffered anddelayed for many more seconds before it is displayed (to eliminate thestalling caused by network congestion). Although time delay is not aproblem with one-way user activities such as watching movies, it is aserious problem for real time “interactive” users, such as users with amouse, controlling a cursor that is a part of the compressed videoimage.

One such example of real time interactive users relates to the remotingof a computer KVM console (Keyboard, Video display and Mouse) over acommunication channel. In these “remote console” applications, keyboardand mouse data are sent from the remote console over the communicationchannel and “switched” to one of a number of “target” server computers,just as if the keyboard and mouse were directly connected to that targetserver. The corresponding video is sent from the target server to theremote console just as if the target server was directly connected tothe remote console's video display. Examples of KVM systems aredescribed in commonly-owned U.S. Pat. No. 5,721,842 to Beasley et al andU.S. Pat. No. 5,732,212 to Perholtz et al, each of which is incorporatedherein by reference.

The communication channel for some KVM systems provides enough bandwidthto transport the uncompressed video because they use dedicated localcables and a dedicated circuit switch. KVM systems adapted to operateover a network via, for example, Internet protocol (referred to hereinfor brevity as “KVM/IP” systems) provide limited and indeterminatebandwidth availability compared to a dedicated local cable-based KVMsystem. Sending keyboard and mouse information from the remote consoleto the selected target server in a timely fashion is one concern withKVM/IP systems. A greater concern is sending the relatively high volumeof video data back to the remote console in a timely fashion. Sincetoday's typical computers output video continuously at over 2 gigabitsper second and remote Internet connections (such as DSL) typicallyoperate at less than 1 megabit per second, video compression ratiosaveraging well over 2000-to-1 are required. Remote Internet connectionsusing dial modems at 50 kilobits per second require even higher averagecompression ratios.

As a remote console user moves their mouse or types on their keyboard toinput new information to the server, those actions must be communicatedto the server and acted upon by the server to create new video images,which are sent back to the remote console user's screen. Delays insending the video back to the remote console user are annoying becausethey create a temporal lag between the entry of the keyboard or mouseinformation by the user and the video response perceived by the user ontheir screen. Delays following keyboard activity are less annoying thandelays following mouse movements, thus the term “mouse-cursor response”is used to describe this problem.

This problem of remote console applications (described above) is notapplicable to some types of typical web browser applications. With webbrowser applications, the video cursor image is created locally on theuser's computer, so mouse-cursor response is always very good even ifthe network is slow at responding with server-generated video images.With remote console applications, network delays affect the mouse-cursorresponse because the cursor is represented as an integral part of thevideo image coming from the server and sent to the remote console overthe network.

In remote console applications, user acceptability for the four types ofvideo loss is the complete opposite from other video applications. Asdescribed above, minimum video time delay is a factor in remote consoleapplications, but video delay is a less important type of video loss inother applications. The importance of resolution loss in remote consoleapplications is also the opposite of other applications because thecomputer screens sent to remote consoles are typically made up of asignificant amount of relatively small font alphanumeric text, manysmall icons and many high contrast sharp edges. Compression systems suchas JPEG or MPEG, that impose resolution loss may be satisfactory formany other applications, but they are not satisfactory for reading smallfont alphanumeric text and images with high contrast sharp edges. Theopposite order of user acceptability also applies to color depth lossand frame rate loss. These two types of video loss are the mostacceptable by users in remote console applications and the leastacceptable in other video applications.

Although existing video compression systems are widely used and wellsuited for a wide variety of applications, a video compression systemoptimized for the best possible interactive computer user experience isneeded.

BRIEF SUMMARY OF THE INVENTION

The present invention is a new video compression system that isoptimized to take advantage of redundancies typically occurring oncomputer screens and also is optimized to take advantage of types ofvideo loss acceptable to real time interactive computer users. In oneembodiment of the present invention, captured frames of computer videoare “encoded” into combinations of five different, uniquely chosen“commands”, which are selected and sequenced based on their ability tomost efficiently compress the captured video. These commands are sentover the network to the “client” where they continuously instruct (orcommand) the “decoder” on how to decompress or decode the commands andrecreate the captured video frames on the remote video display. In aunique way, this embodiment can compress and decompress computer videowithout resolution loss or color depth loss, but with frame rate lossthat is dynamically adjusted depending on available network bandwidth.It also imposes minimal delay during encoding and decoding.

The five commands are; (1) copy old pixels from an earlier frame(sometimes called “no change from an earlier frame,” “no change” orsimply “NC”), (2) copy pixel from the left, (3) copy pixels from above,(4) make a series of pixels using a 2-color set, and (5) make one ormore pixels using a specified color. Each command provides uniqueefficiencies when employed in a hierarchical structure. Also, thecommands are included in comprised of packets that are a fixed length of8 bits or more, such that they can be easily sent, received and decodedwith either software or hardware. The present invention is not limitedto any command or packet length, but preferred embodiments would uselengths that were a multiple of 8-bits (such as 16, 32 or 64) such thatthey would be compatible with popular and commonly available componentsand processors.

In broader embodiments of the present invention, one, two, three, orfour of the types of commands described above are used, alone or in anycombination thereof. For example, the inventor believes that the use ofthe command to make a series of pixels from a 2-color set alone isunique in compressing video that includes a significant amount ofalphanumeric text (such as viewing this document with a word processingprogram). Further advantages and efficiencies are gained when others ofthe commands are added thereto in various combinations. In otherembodiments, one, two, three, four, or all five of the commands are usedin conjunction with any kind of prior art compression system to enhancethe video compression of the known system. For example, MPEG, JPEG, andothers (and all variants thereof (e.g., MPEG2, etc.)) can be used withone or more of the five commands described herein to enhance the videocompression of the prior art compression techniques.

In other embodiments of the invention, referred to as the “gray-favored”color modes, the captured video can be further compressed by takingadvantage of the fact that remote console users accept color depth lossbetter than any other type of video loss. In this mode, each pixel ofthe captured video is converted to the nearest color from a set ofspecifically chosen colors that match typical colors used on computerscreens. Grays are favored in the set of colors since they are favoredon typical computer screens (white and black are included in thedefinition of “grays”).

The present invention can be embodied with the compression encodingimplemented with hardware, with software or with a combination ofhardware and software. Likewise, the decoding can be implemented withhardware, with software or with a combination. The “source” video can becaptured by connecting directly to a video controller chip inside acomputer. Alternatively, the video can be captured from a computer'sexternal analog video output, external digital video interface (DVI) orother external interface. In one embodiment, the video is compressedwith hardware using an FPGA (field programmable gate array) or ASIC(application specific integrated circuit). In another embodiment, thevideo is compressed completely with software before it is made into avideo output stream.

The video compression commands are sent over a network to the remoteconsole where they are decompressed and displayed to the user. Theremote console can be a conventional PC (personal computer), whichdecodes the commands using PC software or it could be a small “thinclient” device built with a low performance microprocessor. In oneembodiment, the commands are all designed to consist of one or more8-bit packets so that they can be easily decompressed with softwarerunning on a low performance microprocessor. Alternatively, a hardwaredevice (such as an FPGA or ASIC) can completely decode the commands atthe remote console. In such a case, the remote console would not requirea computing device for command decoding or a video controller chip fordisplaying the user's video. Such a low-cost hardware (or combinedhardware/software) remote console is referred to below as a“microclient.”

The present invention also has application in computer “blade”technologies, where individual server computers are contained on singlecards, and many of these cards are assembled into a common blade chassisto share a common power supply and central control functions.Conventional cable-based KVM switch technology on the blades can givelocal cable-attached users access to each blade computer, but if usersneed KVM access to the blades over a network, the present inventioncould be included in the blade chassis or on each blade and the videocompression commands could be given to a common network interface in theblade chassis to be sent over the network to the various remoteconsoles.

This invention can thus be employed in generally compressing computervideo, for sending computer video over LANs, WANs, dial-up or any othernetworks, for applications in thin client, microclient, and remoteconsole applications (such as KVM/IP systems).

BRIEF DESCRIPTION OF THE DRAWINGS

The patent application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is a schematic representation of an example embodiment of thepresent invention in a KVM/IP system with the client implemented with PCsoftware;

FIG. 2 is a schematic representation of an example embodiment of thepresent invention showing the internal operation of a hardware videocompressor;

FIGS. 3-10 are tables of the video compression commands in an exampleembodiment of the present invention with 8-bit packet lengths;

FIG. 11 is a chart describing how color depth is reduced in the “7-bitgray-favored color mode” embodiment of the present invention;

FIG. 12 is a color print of test pattern (referred to as the 0-255RGB+Gray test pattern) on the video screen of a computer set for 24-bitcolor.

FIG. 13 is a color print of a client computer screen when the “7-bitgray-favored color mode” embodiment of the present invention is employedand the source video is the test pattern shown in FIG. 12;

FIG. 14 is a schematic representation of an example embodiment of thepresent invention with the video creation software and the videocontroller chip integrated together with the video compressor;

FIG. 15 is a schematic representation of an example embodiment of thepresent invention without a video controller chip, and with softwarevideo compression;

FIG. 16 is a schematic representation of an example embodiment of thepresent invention referred to as a microclient;

FIG. 17 is a schematic representation of an example embodiment of thepresent invention describing the concept of “share-mode”;

FIG. 18 is a chart describing how color depth is reduced in the “5-bitgray-favored color mode” embodiment of the present invention; and

FIGS. 19-24 are tables of the video compression commands in analternative embodiment of the present invention for use with the 5-bitand 12-bit color modes.

DETAILED DESCRIPTION OF THE INVENTION

The present invention can be implemented with any hardware or softwarethat aims to send computer video over a communication channel, includingover an intervening network. One such example embodiment is shown inFIG. 1, which is described by way of example rather than limitation.Indeed other embodiments will be understood once the artisan reviews theinvention, as embodied in the appended Figures and described herein.

In FIG. 1, the KVM/IP system 10 includes a remote console client 11 anda server appliance 14. In the embodiment shown, the remote console 11 isimplemented with PC software in a network-ready PC (which includes akeyboard, video display and mouse). The client 11 communicates via anInternet Protocol network 13, to a target server 15 via the KVM/IPappliance 14. The appliance 14 and the client 11 include standardnetwork I/O hardware and software to permit them to communicate via anyform of Internet protocol connectivity, such as a dial-in, DSL, WAN,LAN, T1, wireless, etc.

In FIG. 1, the appliance acts as an intermediary between the targetserver 15 and the client 11, permitting the client 11 to couple itskeyboard, video display and mouse to the server 15 just as though theclient 11 was directed connected to it. In that regard, the manner andoperation of the system 10 combined with the addressing and switchingcapability of the IP network is typical of KVM switches such as thosesold by the present assignee, and by Cybex Computer Products ofHuntsville, Ala., and by Apex, Inc. of Redmond, Wash.

The client 11 includes software that facilitates the identification ofthe target server 15 (via the appliance 14) such as by a standard TCP/IPaddress. Once communication is established between the client 11 and theappliance 14, the client 11 employs software to send keyboard and mousedata, entered at the client, to appliance 14 via the IP network 13. Theappliance 14 receives the data switched or routed to it, and applies itto the keyboard and mouse ports of the server 15 just as if the keyboardand mouse were directly attached to the server 15. In response, theserver 15 acts on the keyboard and mouse data (via whatever applicationis running on the server 15) to produce new video data, which is outputto the appliance 14 via the video output of the server 15.

Once the appliance 14 receives the video from the server 15, itcompresses it by one of the inventive algorithms described below andtransmits the resulting video compression commands to the client 11 viaIP network 13. Compression can be done with an FPGA, ASIC, or any otherhardware or software in the appliance 14. Alternatively, appliance 14can be “embedded” into the server 15, or it can be eliminated if server15 includes software to perform the compression and send the resultingcommands directly to the IP network 13. Upon receipt, the client 11decodes the commands with PC software and reproduces the target server'svideo on the client PC's screen for viewing by the user. Alternatively,the command decoding could be done with hardware in the client 11.

In the embodiment of FIG. 1, the user should perceive the client PC'skeyboard, video display and mouse as being directly connected to theserver 15, even though the client 11 and the server 15 may be physicallylocated as far away as opposite ends of the globe. Imposing too muchdelay in getting the keyboard and mouse data to the server 15 via theappliance 14, and in getting the video back can impede that objective.The keyboard and mouse require a relatively small amount of datatraffic, which can be transported quickly and relatively efficiently,but the high volume of video data presents a more difficult problem. Tobe effective, the video must be compressed by the appliance 14,transmitted via the IP network 13, decompressed by the client 11, andpresented on the user's screen as quickly as possible. Excessive delayis most evident in mouse-cursor response. Even slight lags between mousemovements and the cursor response presented on the screen are annoyingto the user.

FIG. 2 illustrates an example embodiment of the present invention. Thereare many different hardware and software implementations that thepresent invention can be envisioned within and the embodiment of FIG. 2is not the only such way. After reviewing the present teaching, theartisan will recognize other ways consistent with the breadth of thepresent invention in which to implement the invention.

At the top of FIG. 2, the source video 21 can be in any form, analog ordigital. Most current video controller chips have their video outputavailable digitally for use with flat panel displays, such as used inlaptop computers. The video compressor 23 could connect directly to theoutput pins of the video controller chip 20 or it could connect to anexternal connector on the target server 15. One type of externalconnector is DVI (digital video interface), which is a standard forconnecting digital video to external digital display devices. Any othertype of source video will suffice as well—the invention is not limitedas such.

Optionally, a color depth reducer 22 can be included in the videocompressor 23 to reduce the number of bits defining the color of eachpixel. It does this by categorizing pixels' colors into zones. When thesource video 21 is digital video, the simplest means of color depthreduction is to ignore the least significant bits. For example, 24-bitcolor could be converted into 15-bit color by ignoring the leastsignificant 3 bits of each of the 8-bit red, green and blue signals.Ignoring the least significant 4 bits of each 8-bit color signal wouldresult in 12-bit color. More complex color reduction methods referred toas the 7-bit gray-favored color mode and the 5-bit gray-favored colormodes are described further below and illustrated in FIGS. 11 and 18.

If the source video 21 is an analog video signal, the color depthreducer 22 needs to include an A-to-D (analog to digital) converter.With analog video, each pixel is defined by three analog signals (red,green and blue). The A-to-D converter digitizes the intensity of eachpixel's three signals by detecting what “zone” they are in (very similarto what the digital color depth reducer described above does). A majordifference with analog video is noise. When an analog signal is on theedge of a zone, a small amount of analog noise can make the digitizerbounce back and forth from one zone to another in subsequent frames. Insuch a case, it will appear that the source video 21 is changing even ifit is not. Consequently with an analog input, some method of noisesuppression needs to be used to reduce this “zone bouncing.” Any noisesuppression techniques can be used, but in one example, when the inputsignal is within a zone, it must get out of that zone by at least athreshold amount before it is considered to be in another zone. Thiscomparison of what zone each pixel's signals were in during the previousframe is done for every pixel in the video frame.

Although the several embodiments mentioned for the source video arecontemplated within the present invention, the particular exampleembodiment in FIG. 2 presumes digital video received from a videocontroller in the target server 15 will be the source video. The outputof the video chip 20 is the source video 21, which is a continuingstream of video data. The video controller chip 20 need not becontrolled by any aspect of the present inventions (though theinventions can certainly be employed in conjunction with some video chipcontrol), that is, the video chip 20 will output video in a continuingstream in accordance with its own internal timing.

The source video 21 is the input to the video compressor 23. Of course,other processing devices, such as general or special purpose processorscan be substituted for the hardware video compressor 23. The videocompressor 23 includes at least two frame buffers 24 and 25, and mayinclude many additional frame buffers or frame buffer types foradditional operational complexities and efficiencies. Prior to theclient 11 establishing a connection over the network 29, the sourcevideo 21 is continuously captured (and continuously overwritten) in oneof the frame buffers 24 or 25 (at the instant shown in FIG. 2, framebuffer 25 is active, meaning it is capturing the video).

When a client initially connects over the network 29, the videocapturing stops and the encoder 26 begins reading and compressing thecaptured video data in buffer 25. It starts at the beginning of theframe buffer (which is the upper left pixel on the screen) andprogresses pixel-by-pixel to the end of the frame buffer (which is thelower right pixel on the screen), looking ahead and building the mostefficient sequence of commands. As the encoder 26 builds this series ofcommands (in accordance with the algorithm embodiments described below),the server CPU 27 is sending them to the client 11 via the I/O 28 andthe network 29. After the encoder 26 is finished with the last pixel inthe buffer 25, the frame buffers switch and source video begins to becaptured in the other frame buffer (buffer 24 in this case). This switchoccurs even if the CPU 26 has not finished sending the commands to thenetwork 29. After the switch, the frame in buffer 25 becomes the “old”frame and represents the frame displayed (or soon to be displayed) onthe client's screen.

Since the source video was continuing to run while it was not beingcaptured, it might be half way down the screen or anywhere else in thescreen when the capturing begins. Regardless of where the new captureinto buffer 24 starts, it continues for one full lap until it gets backto the screen position from which it began capturing. The result is onefull “new” frame of video captured from the source video 21. If the CPU27 has not been able to send all the commands from the first compressedframe over the network (possibly due to network congestion or a slownetwork) after the new frame of video is captured, then the capturingprocess will continue overwriting the captured video in buffer 24. Whenthe network is ready for more commands (and at least one frame of videohas been captured), the capturing will stop and the same process thatoccurred for the first frame will continue. However, since the client 11now has its first frame, the encoder 26 will now be able to compare eachpixel in the new frame with each pixel in the old frame and if pixelsdidn't change, the compression will be much better. The same process nowcontinues after at least one frame of new video has been captured andthe network is ready for more commands. This process of continuing tocapture while waiting for the network to be ready lowers the effectiveframe rate to the client depending on network conditions and displayingthe “newest” video takes precedence to displaying “all” of the video. Ineffect, captured video becomes an expiring commodity. The remote consoleusers accept frame rate loss much more than the video delay they wouldhave to tolerate if “all” the video motion was queued and sent later.

Thus, in the present example, the new frame buffer (formerly the oldframe buffer) captures the most recent frame of source video. Then, theold frame (in the old frame buffer) and the new frame (in the new framebuffer) are read by the encoder 26 for the purpose of comparing andcompressing the video. There are alternative methods of capturing andcomparing video frames for compression and all such methods will not bedescribed here.

In the narrower of the embodiments of the present inventions, allaspects of the video encoding described herein with respect to FIG. 3are employed. The detailed description of all of those aspects describedherein with respect to “the invention” or “the inventions” should not beconstrued to mean that the invention requires every aspect of theexample algorithms described. The examples are provided for purposes ofdescribing one example way in which the efficiencies of the inventionscan be realized. Other, broader and narrower, aspects of the inventionmay be realized from the descriptions that follow. Thus, in FIG. 3, fivevideo compression commands are presented for compressing the video readfrom frame buffers 24 and 25. They are, in hierarchical order, (1) copyold pixels from an earlier frame, (2) copy the pixel from the left, (3)copy the pixels from above, (4) make a series of pixels using a 2-colorset, and (5) make one pixel using a specified color. The inventor hasdiscovered that this combination of hierarchical commands providescompelling video compression for computer displays. The first three ofthese commands provide 3 dimensional copying (horizontal, vertical andtime) and the fourth command provides unique efficiencies for screensegments that are comprised of only two colors (such as text).

In the embodiment illustrated in FIG. 3, there are five different videocompression commands. All of the commands are made from either singlepackets or multiple packets, where each packet consists of one 8-bitbyte. The first one to three bits of the first packet of each command isthe operation code (or “opcode”) and they determine the command's basicfunction. The “E” bit is the “extension” bit and the rest of the bits(R, C and P) are the “payload” bits. The general formats of the fivecommands are shown in FIG. 3, and the more detailed formats of them areshown in FIGS. 4-10. For embodiments with different packet lengths, thenumber of payload bits would be different. For example, 16-bit packetswould have 8 additional payload bits.

The lowest hierarchical command, the MP (make pixel) command has a onein the first bit location (bit position seven) followed by payload bits(“P” bits) that define a color (none of the other commands begin with aone). If the number of color bits used is seven, the MP command is onebyte long (as shown in FIG. 3). If the number of color bits used isfifteen, the MP command will be two bytes long, with the first bit ofthe first byte being a one (as shown in FIG. 4). Likewise, if the numberof color bits (P bits) is 23, the MP command will be three bytes long(as shown in FIG. 5), and so on. The MP command is the simplest commandto understand, and also provides the least compression. It says,essentially “make one pixel this color” with the payload identifying thecolor. A popular setting for computer consoles is 15-bit color (5 bitsfor red, 5 for green and 5 for blue). 15-bit color would be supported bytwo-byte MP commands. Since single-byte MP commands have seven payloadbits, they can present 2⁷ (or 128) different colors. The 7-bitgray-favored color mode described further below describes how the sourcevideo can be “reduced” to the nearest of 128 colors widely used oncomputer consoles. The following discussion of the present invention'soperation describes the operation with one-byte MP commands but theinvention is not limited to a specific number of color bits (P bits).

In terms of compressibility, a frame where every pixel is a random colorwould be non-compressible without resolution loss (other compressionsystems, such as JPEG, fractal analysis, etc. could provide compressionwith varying degrees of resolution loss). With the embodiment of FIG. 3,every single pixel in this random frame would be encoded with an MPcommand and if this frame had one million pixels, it would take onemillion MP commands to encode it. If the encoder cannot use any othercommand to encode a pixel, it uses an MP command. Every pixel willalways qualify to be encoded with an MP command. The MP command thustakes its place in the lowest hierachical position in FIG. 3. Being alisting of priority, FIG. 3 indicates that the encoder 26 tries to makethe top command, then the second, then the third, then the fourth, andthen it gets to the MP command as a last resort.

Looking now at the opcodes in FIG. 3, a “one” in bit-position sevenuniquely identifies a make-pixel command. If a “zero” is in bit-positionseven, that command is one of the other four commands shown in FIG. 3,with the next two bits (bit positions five and six) identifying which ofthe other four commands applies. Thus, a 00 in bit locations five andsix indicates a CO (copy old or no change) command, a 01 indicates a CL(copy left) command, a 10 indicates a CA (copy above) command, and a 11indicates a MS (make-series) command. Thereafter, each of these fourcommand types has payload bits that follow the opcode. The payload bitsare the R, C and P bits. The E bits will be discussed below under the MScommand.

The payload bits (R bits) in the CO, CL and CA commands indicate thenumber of times the command operation is repeated. The CO commandinstructs the client that pixels have not changed from pixels currentlydisplayed. Thus, the encoder 26 compares the old and new frame buffersand evokes CO commands when it determines that current pixels in the“new” frame are no different from pixels at the same locations in the“old” frame. Thus, CO commands are sent for portions of the screen thatare not changing in the source video.

The next two commands compare pixels in terms of locations within acommon “new” frame, rather than as between the old and new frame. The CLcommand instructs the client to copy the color from the pixel in theposition immediately to the left in the current frame. If the currentpixel is the first pixel on a video line, the pixel immediately to theleft is the last pixel on the previous line. The CA command instructsthe client to copy the color from the pixel immediately above in thecurrent frame. The CL, CA and CO commands are referred to below as“copy” commands. Other commands may be substituted that provide copyingof pixels with relations within a common frame or as between old and newframes. The presently described commands have particular advantage incomputer video because of the proliferation of horizontal and verticalrectangles and lines that exist in computer video. With horizontallines, for example, CL commands have particular utility and withvertical lines, CA commands have particular utility.

The final command is the MS or make-series command and is itself uniquein the present types of video encoding. The MS command takes advantageof a particular aspect of computer video, namely that large portions oftypical computer screens are composed of only two colors. The classicexample of that in computer video is text information in which largeportions of the screen are made from with a text foreground color on asolid background color. In such cases, the MS command permits theencoder 26 to create a substantial amount of the video without loss ofsharpness in the text, and with very substantial amounts of compression.

Each of the commands will now be discussed in the context of theirpayload structures and in the context of real applications. Aspreviously described, the CO command (FIGS. 3, 6 and 7) essentiallyidentifies that a present pixel has not changed from the pixel locatedin the same location of the previous frame. To further the compression,the payload also identifies not only that a present pixel has notchanged, but also that some number of consecutive pixels didn't change.What that number will be is described below. As shown in FIG. 3 for theCO command, after the three-bit opcode, there are five bits (RRRRR) thatindicate the repeat count of that CO command. These five bits can be setto any binary value between 0 and 31.

Since a repeat count of zero doesn't make sense, one would initiallyassume that these five bits count define up to 32 consecutive pixels ina row that did not change from the previous frame. However, if one-byteMP commands are only being used (instead of two or more byte long MPcommands) a repeat count of one also does not make sense, since aone-byte make pixel (MP) command has the same compression value as an COcommand with a repeat count of one. In that case the repeat countpayload could start with a count of two, such that a payload of 00000means a repeat count of two and a payload of 11111 means a repeat countof thirty-three. With that, a small additional efficiency is provided,namely that an CO command with a five-bit payload identifies the factthat somewhere between two and thirty-three pixels have not changed fromthe frame displayed already.

The preferred embodiment adds still further efficiency. Suppose thatmore than thirty-three pixels have not changed. As shown in FIG. 6, asecond immediately consecutive byte with a 000 opcode can follow a firstbyte with 000 opcode, providing a second five bits to represent from twoto thirty three pixels again. But, instead, the decoder 30 will detecttwo consecutive packets with CO opcodes, and interpret both the five bitpayloads as a single CO command with a ten-bit payload. With a ten-bitpayload, the number of consecutive CO pixels extends from 34 to 1025. Inother words, with just two eight-bit bytes, a frame of over one thousandpixels can be sent to the client. The CO command is escalating in itsefficiency. One can note that there is no other reason to make twoconsecutive packets with CO opcodes other than the fact that a repeatcount over 33 is required. The encoder 26 will not make two consecutivepackets with CO opcodes if a repeat count over 33 is not required.

A two-byte CO command gets inefficient briefly if the encoder 26requires a repeat count of 35 or 36, requiring a second byte. But, oncethe repeat count gets up to a thousand pixels (such as a full line on a1024×768 resolution screen), just two bytes can compress the whole line.Further, if a third CO command follows the second (as shown in FIG. 7),the decoder 30 detects a fifteen-bit payload. If there's a fourth COcommand, it detects a twenty-bit payload. A four-byte CO command canidentify that over one million pixels have not changed, which is morethan is needed for a complete frame with 1024×768 resolution. Thepresent invention is not limited to any particular number of consecutiveCO commands or any video screen resolution, but for present purposes, afive-byte command (that supports up to 33 million pixels) provides arepeat count large enough for a full frame at the highest video screenresolutions currently envisioned.

The CL and CA commands operate the same as the CO command describedabove. They duplicate different pixels (pixels to the left, or pixelsabove) but they have the same structure, a three-bit opcode followed bya 5-bit RRRRR payload identifying a repeat count. Again, each of the CLand CA commands can be sequenced, as shown in FIG. 8 for the CL command,to form 10 bit, 15 bit, 20 bit, or longer payloads.

The hierarchical priorities between the CO, CL and CA commands onlyapply if two or more of those commands simultaneously qualify on thecurrent pixel. If the encoder 26 determines that the CO commandqualifies on the current pixel and no other copy command qualifies, theencoder temporarily ignores the other copy commands and continues tocompare pixels from the old and new frames, to determine how many pixelsin a row the CO command qualifies for. The encoder 26 would do the samething if it discovered that the CA or CL commands alone qualified on acurrent pixel. At the first instance that the identified (CO, CA or CL)condition is no longer true, the encoder 26 sends one or moreconsecutive commands of FIG. 3 and then evaluates the next pixel forencoding. In other words, once the encoder 26 determines that one repeatcount condition is true for a given pixel, and only one repeat countcondition is true for a given pixel, it ignores all other commandevaluations until the current repeat count condition is no longer valid.When that occurs, it creates the command (opcode and repeat count) andsends it to the client.

As long as one copy command (CO, CL, or CA) qualifies, the encodercontinues with it until it no longer qualifies. Then the encoder endsthat analysis and creates the appropriate bytes. If, however, multiplerepeat count conditions (CO, CA or CL) initially qualify on the samepixel, the encoder just starts counting consecutive pixels for whichthose conditions apply. As long as one of these commands qualifies, thecounter continues to run. Eventually, the encoder will choose only onecommand that applied for the full repeat count so it only counts onecounter. It does not need to run three different counters, one for eachcopy command. Then, as the encoder continues to count, it will discoverthat some commands no longer qualify. When that occurs enough times sothat no command type is “left standing,” the encoder 26 creates theopcode for the last surviving command, together with the repeat countidentifying the number of pixels that qualified before the lastsurviving command failed to qualify.

As an example, suppose for a current pixel, CL, CA and CO commands allqualify. The encoder records that and begins counting. In the nextpixel, the encoder determines that all still apply, and so incrementsthe counter to two. The process continues identically until, in theseventh pixel, the CL condition no longer applies. The encoder 26 dropsCL out of the running and continues incrementing the counter.Continuing, suppose in the 14^(th) pixel, the CA condition becomesfalse. The CO command is the last survivor, but the encoder still doesnot stop counting. It continues incrementing until, suppose in the51^(st) pixel, the CO condition becomes false. At that point, theencoder 26 sends two consecutive bytes to the client 11: 00000001 and00010000. The first byte indicates a CO condition (opcode=000) for whatfirst appears to be a repeat count of three (recalling that a “zero”specifies a repeat count of two). But, when the decoder 30 looks aheadto the next byte, it sees that the consecutive CO commands are to beread together to form a ten-bit word. (Note that the decoder 30 willalso look to the next byte beyond the 00010000 byte before decoding theword, to be sure that a third CO byte does not follow the second one).The ten-bit word: 0000110000 equates to a repeat count of 50. Thisseries of two CO commands instructs the decoder to not change the next50 pixels from the colors they were in the previously sent frame.

Once a copy command becomes the last one standing, the opcode for thenext command is determined. When this last standing command no longerqualifies, the repeat count for that command is determined. At thatpoint, the encoder also determines how many bytes are necessary toidentify the repeat count. If the count can be provided in five bits,the encoder generates a one-byte command. If ten bits are required, theencoder generates a two-byte command, and so forth. This aspect of thepreferred embodiment is advantageous because it capitalizes optimally onthe identification of the longest possible repeat counts. In fact, onecan envision other copy commands, other than CA, CL and CO, whichidentify pixels based on other relational aspects.

The hierarchical priorities between the CO, CL and CA commands apply iftwo or more of those commands are equally last standing. In that case,the encoder resorts first to the copy old command. The copy old commandpresents the least burden on the client because the result is onlyskipping over pixels. On the other hand, the client has to work to copyfrom above or to copy from the left. As between these two copy commands,the copy left is higher priority than copy from above, again because itpresents less of a burden to the client. With a copy left, the clientonly needs to read the immediately preceding pixel once and write it anumber of pixels. To copy from above, however, relies on reading anumber of pixels from the video line above and writing to a number ofpixels.

On the other hand, if the client were implemented with hardware ratherthan software, the copy command priority may not matter because thehardware may be dedicated to processing commands. The preferredembodiment minimizes the load on a software client by prioritizing thecopy commands.

The fourth command type (and the highest priority of non-copy commands)is the MS (make-series) command shown in FIGS. 3, 9 and 10. Based onanalysis of the compression of typical computer screens, the make-seriescommand ends up contributing a great deal to the efficiency of thecompression. The theory on the MS command is that text, no matter whatcolor it is in, is almost always in a two-color mode. Indeed, theinventor examined typical computer screens and determined that largeportions of text and other areas of the screen can be defined with longMS commands. The MS command provides great efficiency in compressing thetext portions of icons, of documents, of labels, and of tool bars. Othercompression schemes either do not provide the requisite compressionefficiency or do not provide the sharpness demanded by users who have toread text material on the screen.

Take, for example, the instance where a user is scrolling through textsuch that from one frame to the next, the text is just shifting up alittle bit. From the compressor's point of view, each frame is a newgroup of pixels that need to be encoded. The compressor may get somerepeat count efficiency by writing CO commands for areas around the textwindow, but when it hits the adjusted text, repeat count compressionbecomes inefficient because long repeat counts don't occur. The inventorhas added efficiency for those text-type areas where copy commands don'twork well. Exactly how those MS commands add compression efficiency willnow be described.

First, like before, the three-bit opcode identifies the MS command. Thefirst opcode bit (0) indicates that the command is not a make-pixelcommand. The next two bits (11) identify the command as a make-seriescommand. Opportunities to evoke the MS command are identified by theencoder looking ahead four pixels. The artisan should note that the copycommands require no look-ahead operation (though look-ahead operationscan be added for the sake of providing additional features). With the MScommand, alternatively, more or less pixels can be used for thislook-ahead operation. As will be seen the number of pixels in the lookahead should be chosen strategically to be (1) large enough to ensurethat repeat count coding won't be more efficient, (2) short enough tomake the MS command appropriately applicable, and (3) valued as aninteger that accommodates the word length being used. Solely forpurposes of example herein, four pixels will be described. MS commandsare invoked when the encoder determines that, within the next fourpixels, two conditions occur: (1) that a CO, CL or CA command is notgoing to qualify, and (2) all the pixels in those next four pixels arelimited to two different colors. The “extended” MS command, shown byexample in FIGS. 9 and 10, extends the MS operation, but only the firstbyte includes the opcode in bits 5, 6, and 7. The extended MS command isdescribed further below.

As previously described, the MS command is used for a series of pixelsthat are a combination of two different colors. The two colors that areincluded in the set of available colors are the color from theimmediately preceding pixel (color 0) and the most recent differentcolor pixel before that (color 1). Of course, other methods ofidentifying the two pixel colors for the MS command can be employed froma variety of options, including strict identification of the colors,identification from selected positions in the present frame, or theprevious frame, identification from a lookup table of two-color sets,etc. In the preferred embodiment, the two colors are derived from theimmediately preceding two different color pixels, which may have beenencoded using make-pixel, copy-above, copy-left, or copy old commands.The MS command does not care how these two pixels got there, just thatthey will become the two colors for the upcoming MS command's series ofpixels.

The MS command with the two-color set described above is advantageousbecause it does not require bytes with any color identification bits.That is, the MS commands do not include bits that identify which colorsare being used, only which of the two previously identified colors arebeing used in the series. So, for example, when the encoder reaches thebeginning of some text, such as the top left corner of a black letter“H” on a white background, the first pixel on the top left corner of the“H” may be defined with a black MP (make-pixel) command followed by a CL(copy-left) command for a few pixels. As the top center and top right ofthe H are found by the encoder's look ahead, the encoder will create amake-series command because it is detecting only two colors (text andbackground) in the coming pixels.

As shown in FIG. 9, the first MS command byte has a three-bit opcodefollowed by an “extension” bit (in bit position 4) that indicates thatthis command is extended to the next byte. If the extension bit is zero,the MS command is not extended, and it ends after the first byte. Insuch a case, the four “C” bits in that byte provide the two-colorpattern for four pixels and then the present series ends. If, however,the extension bit is on, then another whole byte of MS data will followthe present one. Thus, in FIG. 9, the second byte is an “extendedcommand” byte. Because the extension bit is present in the precedingbyte, the next byte need not include the three-bit opcode. The identityof the extended command thus comes not from an opcode in the presentbyte, but from the extension bit in the preceding byte. The resultprovides seven bits for make-series data for every byte following thefirst byte. Each extended command byte includes its own extension bit(in bit position 7) that identifies whether or not a next byte is anextension byte. This extension can go on as long as the E-bits are on.When the E-bit goes off, the present series stops. The series of FIG. 10indicates an example of a 13 byte long MS command that will define aseries of 88 consecutive pixels.

As the decoder receives the make-series bytes, it begins immediatelycreating pixels for the client screen, as follows. After reading theopcode 011, the decoder realizes that a make-series is beginning. Itreads the color of the preceding pixel and defines that color as “color0”. Then it reads the most recent different color pixel before that anddefines that color as “color 1”.

The decoder then reads the E-bit to determine whether the series is onebyte, or more. Finally, the decoder reads bits 0-3, in order, andcreates pixels from the two available colors based on the binary statusof each pixel. For the first byte, the decoder will create four pixels.For example, if the first MS byte is 01110110 and color 0 is black andcolor 1 is white, the decoder will create four pixels (0110) of black,white, white, and black. Then, because the E-bit is set to 1, thedecoder will look to the next byte to create seven more black and whitepixels.

The first byte of an MS command, in the preferred embodiment, createsfour pixels (eight bits minus three opcode bits minus one extensionbit). If the encoder finds that less than four pixels are present in theseries (i.e., more than two colors are present in the next four pixels),then the MS command cannot be used in the preferred embodiment. Further,if a first extension byte (a second cumulative byte) of MS command is tobe used, the encoder must look ahead to find that the next sevenconsecutive pixels qualify for MS status (i.e., all from only two colorchoices and no copy command applies). Then, as shown in FIG. 9, the fourC-bits in the first byte will identify the first four pixels of theeleven-pixel series, and the seven C-bits in the second byte willidentify the next seven pixels in the eleven-pixel series. Thereafter,new MS extension bytes are used only when whole multiples of sevenpixels can be added to the series. Hence, as previously described, theencoder “looks ahead” before encoding any MS command byte, in order to:(1) determine whether the first four pixels qualify for MS treatment,and (2) determine whether additional bytes of seven pixels will qualify.

As will now be understood, the MS command defines sequential pixels,using sequential bits, such that each bit corresponds to each pixelbeing either color 0 or color 1. In effect, the C-bits of the MScommands are like a pixel train.

As previously described, the encoder in the MS mode is always lookingahead and won't set the E-bit unless it sees that it will have enoughpixels in the coming series of pixels to fill the next seven bits of anext extension command byte. If the encoder looks ahead and encounters acolor different from the two-color set, within the next seven pixels,then it ends the make-series command with the current byte (writing astop bit into the E-bit of the current byte).

In one embodiment, the encoder is doing comparisons for all of thecommand types for all of the pixels all of the time. In that case, thecomparisons are always running in parallel, and are always running forall commands. When one of the command types recognizes its ownapplicability, the encoder flags it and determines (based on othercomparisons and priorities among the commands) which of the commandtypes is the optimum one for the present situation. In the embodiment ofFIG. 2, for example, the video compressor 23 is, for every single pixel,looking for the applicability of each of the five command types, andlooking ahead in accordance with the MS command requirements.

The embodiments described above do not work well on the firstpresentation of photographs on a screen, because photographs require arelatively large number of make-pixel MP commands. Until a still photois sent once, the encoder does not create many copy commands, whichcreate better efficiencies. Of course, after a still photograph isinitially sent to the client, the encoder will generate CO commands forthose parts of the screen on subsequent frames. The present embodiments,while less applicable to photographic information, provide extraordinaryefficiency in the application of computer console screens, where manyvertical and horizontal lines frequently qualify for copy commands andscreens include a significant amount of text.

The embodiment of the present inventions referred to as the 7-bitgray-favored color mode provides a novel and creative use of themake-pixel (MP) command vis-a-vis color and gray intensity charts. Thismode aims to achieve the maximum performance from the 7-bit payload of aone-byte MP command. As shown in FIG. 11, each of the incoming colors(red, green and blue) ranges in intensity anywhere from 0 (darkest) to255 (brightest). Some existing computer console color depth reductionschemes use six total bits to define all colors (two bits are providedfor red, two for blue and two for green), resulting in four differentshades of red, four different shades of blue and four different shadesof green. The combination of 4³ is 64 possible color combinations.

Grays are also important in computer applications, and consist of eachcombination in which R, G, and B are present in equal intensity. Thesix-bit color scheme described above, by default, provides four possibleshades of grays. While the four shades of R, G, and B may provideacceptable color depth, the limited numbers of gray shades proveunsatisfactory for gray-scale depth.

In an example embodiment (though not a limiting one), the number ofcolors can be increased beyond 64 while also increasing the number ofgray shades by a greater proportion than the colors were increased. Todo so, a “popularity of use” for all colors (including grays) isassigned based on a collection of arbitrary computer console screens, apredetermined color selection, etc. and, from that, a frequency tableidentifies which colors (and grays) are considered most popular. In FIG.11, the binary and decimal intensity levels (from 0-255) are shown inthe left columns, followed by “popularity of use” ranking. In thatcolumn, the longer the line, the more that color was identified in thepool of typical computer screens. As shown, the zero intensity is usedoften, 63 and 64 are used often, 127 and 128 are used often, 191 and 193are used often and 255 is used often.

The inventor found that grays were more popular than non-grays ontypical computer screens. For example, the scroll bars are gray, thetoolbars are gray, and when a “button” is pushed, the edges aroundbuttons are changed to different shades of gray. Black and white areshades of gray and are very frequently used. Computer screens use a lotof different shades of gray, and the shade varieties are important forcontrast. As color depth was taken away for video compression purposes,the first place that video quality suffered was on the grays. As itturned out, the actual colors were less critical. For example, it wasless important how red a red was or how green a green was. But whendepth of grays went away with the color depth reduction scheme,important contrasts like when a “button was pushed” on the screen werelost.

By looking at the popularity of colors, by providing five shades each ofR, G, and B, and by finding code locations to add more grays, thepresent embodiment provides all of the colors needed for good colorcontrast while adding excellent gray scale contrast. First, a set ofpopular red, green, and blue intensities was selected. For the examplein FIG. 11, each of red, green and blue can occur in one of five of themost popular intensities: 0, 64, 128, 192 and 255. Those become the fivedifferent shades provided for each of the colors, namely five shades ofred, five shades of green, and five shades of blue. The total number ofcolors available using those five shades is: 5³=125. Within that 125colors will automatically be five shades of gray, specifically: (1) R,G, and B all equal 0, (2) R, G, and B all equal 64, etc. Five grays isbetter than four, but it is still not as good as one might desire.

For that reason, additional grays can be coded into a “hidden” area ofthe pixel encoding. As shown in FIG. 4, the MP command defines the Red,Green and Blue intensities with seven bits. 128 states (2⁷) can bedefined by these 7 bits but, using the five-shade popular color schemedescribed above, only 125 colors are identified. The present exampleuses the leftover three states (128 less 125) for three additional grayscales. Now, instead of five shades of gray (RGB=0, 64, 128, 192, and255), three additional shades of gray (RGB=96, 160 and 224) areincluded. The eight grays are shown in the far right column of FIG. 11.

FIG. 12 is a color print of a test pattern (referred to as the 0-255RGB+Gray test pattern) on the video screen of a computer set for 24-bitcolor. The test pattern has horizontal bars of pure red, pure green andpure blue, increasing from zero (darkest) to 255 (brightest). It alsohas a bar of pure gray (equal amounts of red, green and blue) increasingfrom zero to 255. FIG. 13 is a color print of a resulting client screenwhen the “7-bit gray-favored color mode” embodiment of the presentinvention is employed and the source video is the test pattern shown inFIG. 12. In the end, the 7-bit gray-favored color mode accuratelydisplays the most popular five shades of red, green and blue andprovides more levels of grays than the artisan would expect from 7-bits.

Compared to the prior art six-bit color schemes, the 7-bit gray-favoredcolor mode provides better color quality, with twice as many grays(eight versus four). The 7-bit gray-favored color mode has particularapplication in the computer arts where high color depth is not ascritical and has even more particular application in the networkadministration arts. Network administrators are frequently maintainingservers that are not proximate to the administrator. Still, theadministrator needs to access servers and interact with the servers inreal time. Getting the video from a server to a network administrator asquickly as possible after keyboard or mouse inputs is important. Andprior art video schemes that return video in such poor color or grayquality, or are too slow to keep up with keyboard and mouse inputs areunacceptable. The present compression system with the 7-bit gray-favoredcolor mode provides excellent color quality and exceptional gray scalequality for the network administrator, who needs good video for thefunctional aspects of a computer interface (buttons, bars, etc.).

In another embodiment of the present invention, the color depth isdynamically increased or decreased as a function of the source videocontent and/or network bandwidth availability. The video compressionencoder would notify the client that the length of the MP commands wouldbe increased or decreased and all other commands would remain the same.Since the MP commands are the lowest priority and are relativelyinfrequent, the expansion to two or more bytes for each MP command doesnot dramatically increase the network traffic generated from using mostcomputer screens. Viewing images such as photographs would increase thenumber of MP commands and increase the difference. Tests have shown thatincreasing the MP command from one to two bytes only increases trafficon typical computer screens by 30%.

In another embodiment of the present invention, network traffic can beminimized by not sending data if there are no changes to the sourcevideo from the previous frame sent. In this embodiment, when the encoder26 recognizes that no changes have occurred, there is no need to sendcommands because when client 11 receives no commands, no change is madeto the client screen by default. In another alternative embodiment,after some period of time (for example one minute) the server softwaresends a message to the client to let the client 11 know that theconnection is still working and the screen has not changed.

In the embodiment described in FIGS. 1 and 2, the source video comesfrom video creation software and a video controller chip, both locatedin the target server 15. Another example embodiment is to have thesource video come from video creation software and a video controllerchip, both integrated together with the video compressor. An example ofsuch an “embedded” fully integrated system is depicted in FIG. 14.

Another alternative embodiment is to compress the video (using the sametypes of video commands described above) completely with software thatinterfaces directly with the video creation software, eliminating theneed for a video controller chip. An example of such a pure software“controller-less” embodiment is depicted in FIG. 15.

In the earlier example embodiments, the command decoder was implementedwith PC software. An alternative embodiment would implement the decodercompletely with hardware or with a combination of hardware and a smalllow-cost low-performance microprocessor. This “embedded” decoder wouldoutput its video directly to a video display (without a PC or videocontroller chip) as shown in FIG. 16. This “microclient” could alsocontain keyboard and mouse interface circuitry and could also beintegrated into the video display. A microclient would be applicable inapplications where it is desirable to have all of the workers computersout of the main work area and in a back room. In the work area, onlykeyboards, monitors and mice would be present on desktops. When a workermoves from one place to another, they could log onto their computer (orany other computer they were permitted to) from any microclient.

Another example aspect of the present invention will now be describedwith respect to FIG. 17. If a second client 16 is added (the same asclient 11) which also has the same client software and is also connectedto the IP network, the server appliance 14 could sent the same videocompression commands to both clients, permitting both clients tosimultaneously “share” access to target server 15. Usually, in this“share mode,” one client is accessing the server 15 and the other clientis watching. The example may occur when a client 11 is employing aserver and is in some operational error that the client user wishes anetwork administrator (who is at another location) to see. This isreferred to as the “help desk” mode. The share mode is taken to greaterextreme in cases where video is multicast, as to a group of traineessitting at multiple respective client remote consoles 17 and 18.

In share mode over the Internet (especially with a large number ofsimultaneous users) it is advantageous to employ UDP communicationinstead of TCP communication. As the artisan will understand, UDP usesunacknowledged datagrams, while TCP's datagrams are acknowledged. Theimplosion of acknowledgements with a large number of simultaneous sharemode users could flood the server appliance. The advantage of TCP isthat no data is lost because everything is sent and re-sent untilacknowledged. With video, however, the user cares less about what islost than about continuous video flow. In other words, just because thescreen flickered due to a lost frame, does not mean that the userdesires that the video return back to the missed frame and start over.The present invention can be employed with TCP, UDP, or any otheracknowledged or unacknowledged protocol.

The applicant notes that a disadvantage of UDP protocols is that theycan contribute to denial of service attacks that maliciously occur onthe Internet. Because UDP is unacknowledged, traffic can flood a serverwith UDP datagrams. To prevent that, firewalls often block UDP. Usingthe present invention in the example embodiment employing UDP requiresthe acceptance of UDP datagrams, however training room environments andother applications for large numbers of share-mode users would typicallybe inside a facility behind the firewall.

In still another embodiment, data encryption is applied to the videocompression commands, such that the compressed computer screens beingtransmitted are secure from monitoring. Any encryption technology can beemployed, but an encryption technology, such as AES encryption, thatcould be implemented in the same video compressor 23 along with thevideo compression encoding would be much more desirable from animplementation viewpoint than a separate data encryption device.

The inventor presented the combination of command structures describedabove combined with the 7-bit gray-favored color scheme as a preferredembodiment because this combination was an optimization of trade-offsthat were well suited for computer administrators working in a KVM-styleserver management environment. Rearranging the command opcodes andchanging the color scheme can reduce network bandwidth requirements orincrease color depth for other environments.

For example, if only five bits of color are used to implement the 5-bitgray-favored color mode shown in FIG. 18, it would be advantageous toexchange the opcodes between the MS command and the MP command, as shownin FIG. 19, because the single bit opcode would be “wasted” on an MPcommand with only five P bits. In that embodiment, the single bit opcodewould be better used to enhance the efficiency of the MS command. Italso would eliminate the need for the MS command's extension bit (Ebit), since simply sending subsequent MS commands could extend an MScommand, as shown in FIGS. 20 and 21. This alternative combination ofcommand structures and 5-bit color offers less color depth but improvedperformance on screens with a significant amount of text (because ofmore efficient MS commands), however it offers the same number of grays(8) as the 7-bit color mode described above.

Another embodiment optimized for applications that require more colordepth, uses the same alternative arrangement of opcodes shown in FIG.19, but the MP command is either one or two bytes long as shown in FIGS.22, 23 and 24. When it is two bytes long it provides 12-bit color (4red, 4 green and 4 blue) as shown in FIG. 23. When it is one byte long,it provides 4 bits of payload that define 16 shades of gray (red, greenand blue all are equal) as shown in FIG. 24. The “A” bit (or “all” bit)in FIG. 22 indicates that all three colors are equal to the value of the“P” bits and the command is limited to one byte. Effectively, thevariable length MP command is gray-favored in that less network trafficis generated from one-byte gray commands. In another embodiment, the4-bit payload of the one-byte MP command represents the 16 most popularcolors instead of 16 grays. The 16 most popular colors could bedetermined by recent usage statistics with MP commands, or by a pre-setlist of 16 popular colors. Also, the same advantages of the moreefficient MS command in the 5-bit color mode described above areincluded in this 12-bit color mode. The close similarity of the 5-bitand 12-bit color modes described here would allow an embodiment thatdynamically switched between 5-bit and 12-bit color depending on sourcevideo content and/or available network bandwidth. Other rearrangementsof the commands, similar to those shown to accommodate the 5-bit and12-bit color modes, could also be advantageous for improved performancein other applications or other environments.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. Apparatus, comprising: an encoder including an input to sequentiallyreceive a stream of pixels of video data that: (a) compares a colorpixel of the video data to a number of next consecutive pixels in thestream and determines if a pre-defined number of said color pixel andnext consecutive pixels are drawn from a set of only two unique colorsand if so, color pixel and the next consecutive pixels into at least onepayload of a string of different single bit codes in which each of thedifferent single-bit codes points to respective ones of the two uniquecolors and the string of two different single-bit codes includes a firstsingle-bit code corresponding to the color pixel and subsequentsingle-bit code in the string corresponding in like order to the nextconsecutive pixels in the stream, and if said condition (a) does notapply, the encoder (b) compares the color pixel to a plurality ofrespective reference pixels having unique location types to determine ifa similarity condition exists between a value of the color pixel and avalue of one or more of the respective reference pixels by firstlycomparing (i) the color pixel with a first respective reference pixelhaving a pre-established direction and distance from the color pixel inthe same frame and by secondly comparing (ii) the color pixel with asecond respective reference pixel having a pre-established uniquedirection and distance from the color pixel in a contiguous ornon-contiguous prior frame of the video data, and thirdly counting anumber of pixels immediately following the color pixel for which atleast one of the conditions (i) and (ii) yields a continuous stream ofsimilarity conditions, and wherein the encoder encodes the color pixeland said number of pixels following the color pixel using a codeidentifying said condition (i) or (ii) that applies for the greatestnumber of consecutive subsequent pixels beginning with the color pixeland information identifying the number of pixels for which thecontinuous stream of similarity conditions applies.
 2. Apparatusaccording to claim 1, wherein: when said encoder fine that the number ofconsecutive subsequent pixels for which two or more location types areequal, selecting the selected location type based on a predeterminedhierarchy between said two or more location types.
 3. Apparatusaccording to claim 1, wherein: said location types include: a pixellocated to the left of said color pixel in the same frame; a pixellocated above said color pixel in the same frame; and a pixel located inthe previous frame at the same location as said color pixel.
 4. A methodof compressing a video stream to be displayed at pixel locations on ascreen, comprising: (a) sequentially receiving frames of informationfrom the video stream comprising sequential series of respective pixelidentifiers; (b) for a first received pixel identifier, comparing thefirst pixel identifier with; (i) an adjacent-pixel identifier adjacentthe first received pixel on the screen; (ii) an above-pixel identifierabove the first received pixel identifier on the screen; and (iii) anold-pixel identifier at the sane screen location as the first receivedpixel identifier but on a previous screen; and (c) counting a number ofpixels from the first received pixel identifier for which at least oneof said conditions (i), (ii), and (iii) yields a continuous stream ofidentity conditions; (d) in an encoder, encoding a data packet having: acode identifying one of the three conditions (i), (ii), (iii) whichprovides the longest said continuous stream, and information identifyingthe length of said longest continuous stream.
 5. A method oftransmitting frames of video information, comprising the steps of:receiving serial video information; in an encoder, creating commandsencoding the serial video information into a series of video commandfunctions by analyzing change relationships between current values ofsaid serial video information and prior values of said serial videoinformation, the commands including (1) commands to copy a prior pixelvalue for a prior pixel having a predetermined location in the serialvideo information relative to a current pixel, (2) commands to identitya current pixel value by its color definition, and (3) commands toidentify a subset of current pixel values from only two colordefinitions associated with two distinct prior pixel values locatedimmediately prior to the subset of current pixel values in the serialvideo information; and dynamically and automatically adjusting a frametransmission rate of said change relationships, wherein the frametransmission rate is automatically and dynamically reduced bycontinually overwriting the encoded current pixel values in accordancewith the created commands until a transmission of the encoded currentpixel values occurs, in order to preserve a color depth and resolutionassociated with the current pixel values at a cost of the frametransmission rate.
 6. A method according to claim 5, wherein said priorvalues are encoded to optimize encoding by selecting for given pixelsthe more efficient encoding command of (1) commands to copy prior pixelvalues and (2) commands to identify a current pixel value by colordefinition, where the more efficient encoding is base on a determinationof a number of packets required by each of said commands to encode saidgiven set of pixels.
 7. A method according to claim 5, wherein the stepof dynamically and automatically adjusting the frame transmission rateincludes, when an available transmission capacity reduces, steadilymaintaining a resolution quality of said video information whileadjusting said frame transmission rate to accommodate said reduction inavailable capacity.